1. Field of the Invention
The invention is related to the field of magnetic disk drive systems and, in particular, to a lead contact structure and methods of generating the structures for extraordinary magnetoresistive (EMR) elements.
2. Statement of the Problem
A magnetoresistive (MR) read element based on extraordinary magnetoresistance (EMR) has been proposed for magnetic recording hard disk drives. Because the active region in the EMR element is formed of nonmagnetic semiconductor materials, the EMR read element does not suffer from the problem of magnetic noise that exists in giant magnetoresistive (GMR) elements and tunneling magnetoresistive (TMR) elements, both of which use magnetic films in their active regions.
The EMR read element includes an EMR structure that is fabricated on a substrate as a mesa comprising a semiconductor heterostructure. The EMR structure referred to herein comprises layers of semiconductor material. A subset of the layers of semiconducting material comprises a 2D electron or hole gas which is referred to herein as the EMR active region. A pair of voltage leads and a pair of current leads are formed on one side surface of the mesa in contact with an active region of the EMR structure, and an electrically conductive metal shunt is formed on an opposing side surface of the mesa in contact with active region. In the absence of an applied magnetic field, injected current through the current leads passes into the active region and is shunted through the metal. When an applied magnetic field is present, current is deflected from the shunt and travels a longer distance through the active region. Because the semiconductor is much more resistive than the shunt, the electrical resistance of the device increases. The change in electrical resistance due to the applied magnetic field is detected across the voltage leads. EMR is described by T. Zhou et al., “Extraordinary magnetoresistance in externally shunted van der Pauw plates”, Appl. Phys. Lett., Vol. 78, No. 5, 29 Jan. 2001, pp. 667-669. An EMR element for recording head applications is described by S. A. Solin et al., “Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording”, Appl. Phys. Lett., Vol. 80, No. 21, 27 May , 2002, pp. 4012-4014.
One problem for fabricators of EMR read elements is providing low ohmic contact resistances between the active region of the EMR structure and the current and voltage leads. As is illustrated in FIG. 1, a typical lead is formed on one side surface of the mesa. One end of the lead extends above the top of the EMR structure while the other end extends outwardly from the side surface of the mesa to provide a contact point. The contact resistance area is determined by the thickness of the active region and the width of the lead contacting the active region. The problem is magnified as the EMR read elements are fabricated on the sub-micron scale, as the thickness of the active region and the width of the leads are decreased. Assuming a contact resistance area product of 1E-7 Ohm·cm2, a 20 nm thick active region, and a 20 nm wide lead, the contact resistance would be 25 kOhms for each lead. This contact resistance far exceeds the typical resistance of EMR elements, which is a few ohms.
Another problem is that the leads of a typical EMR read element are not planar with the top of the EMR structure. Magnetic recording applications for EMR read elements require that the active region (the 2DEG) of the EMR read element be in close proximity to the disk surface. Any non-planarity (i.e., leads higher than the surface of the EMR structure) requires a larger spacing between the disk media and the EMR structure since the top surface of the leads now set the minimum spacing rather than the top surface of the EMR structure. The resulting increased spacing reduces signal and resolution characteristics of the EMR read element. Furthermore, in one mode of operation the EMR read element is riding on an air-cushion with its top surface being the air bearing surface. For this mode of operation, a generally planar top surface is desirable to obtain a flyable EMR read element.